Question

What is the percentage dissociation of $0.1$M solution of acetic acid? $(K_a={10}^{-5})$

• A. $10\%$
• B. $100\%$
• C. $1\%$
• D. $0.01\%$

Answer 1

The correct option is D $0.01\%$

$K_a$ is the dissociation (or ionisation) constant of the acid HA and $\alpha$ is its degree of dissociation.

$\alpha =\frac{\left(C_{\alpha }\right)\left(C_{\alpha }\right)}{(1-\alpha )}=\frac{C_{\alpha }^2}{1-\alpha }$

This is known as Ostwald’s dilution law equation. If $\alpha <<1$ then the above equation may be written as:

$\alpha =\sqrt{(}\frac{K_{\alpha }}{c})$

$\therefore \sqrt{(}\frac{{10}^{-5}}{0.1})={10}^{-2}=0.01$